Photographic printing emulsion and its production



Patented May 21, 1935 UNITED STATES PIIoToGnAPIIIo PRINTING EMULsIoN AND ITS PRODUCTION William Ambler Berry, Knutsford, England, as- .sig'nor to Ilford Limited, Ilford, England, a

British company No'Drawing. Application March 15, 1934; Serial N0.'715,779. In Great BritainMarch 22 1933 8 Claims.

' This invention comprises improvements in or relating to photographic emulsions of the development type.

Photographic emulsions may be divided into two main types. One type comprises the printing-out emulsions which consist essentially of silver chloride together with an excess of a soluble silversalt such as silver nitrate or a silver salt of an organic acid, e. g. silver citrate, lactate, ,or oxalate. With such emulsions'an image is obtained simply by exposure to light. 'The other type comprises" the development emulsions which consist chiefly of silver chloride, silver bromide or combinations thereof, and do not contain any soluble silversalts; A development emulsion does not, even on prolonged exposure to light, give a useful visible image, but requires development after exposure (insuflicient in itself to give a visible image) to produce the useful visible image. With certain development emulsions including those of the so-called gaslight'type one usually obtains an image which is substantially black and it is known to incorporate substances in these emulsions or to vary theconditions' of development in order to modify the quality of the blackness of this image produced by. development. Also, the tone or colour of such developed images may be modified: by treatment in a toning bath to give an image of substantially different chemical composition from that of the developed image, for example in a sulphide solution which gives sepia tones by conversion of the silver image into silver sulphide. It'is an object of the present invention to provide a development emulsion which has selftoning properties and produces upon development and fixation a toned image comparable with one obtained on printing out paper when printed and toned in the usual way. British Patent No. I

phenomena imparting self-toning qualities to 10,051 of 1906 describes a self-toning silver chloride printing-out paper prepared from an emulsion containing chloride of gold to'which a salt or salts of leadth ave been added for the purpose of improving the toning properties. .That specification, howevenis concerned only with printing-out emulsions, while the present invention, on. the other hand, is concerned only with development emulsions which are distinguished from printing-out as indicated above.

The present invention comprises a self-toning "development emulsion in which the light-sensitive "salt consists mainly or exclusively of silverlchloride without any soluble silver salts-and which contains self-toning ingredients rcomprising a and fixing.

gold salt and a lead salt with or without a thiocyanate. 'f V In putting the present invention into effect it is preferable when the thiocyanate is omitted from the emulsion that it should be added to the The invention also includes a process for the production of a photographic development emulsion comprising forming an emulsion containing essentially gelatine and silver chloride precipitated in situ and then adding atoning agent.

The invention further; includes a method of producing a toned image which consists in ex-. posing to light a paper bearing a self-toning development emulsion, developing the exposed paper and finally toning and'fixing the image in one operation by immersing the print in a solution of sodium thiosulphate.

In'U. S. specification Ser. No. 631,272: photographic emulsion is described having printingout self-toning properties, that is to say, which on exposure to light produces a visible image which on subsequent treatment in a. fixing bath gives an image toned according to, duration of thetreatm ent. According to the specification an essential ingredient of the emulsion, is a salt of manganese; Further, the specification states that the emulsion is also amendableto'the production' of a seli-toned image by development It has now been found that the omission of themanganese salt in the preparation of such an emulsion, whilst destroying the printing out properties of the emulsion, does not impair the self-toning properties and that images producedby theaction of light onthese emulsions can be developed and subsequently toned in a fixingbath.

The theories underlying the nature of the developed photographic images are not at present thoroughly understood and therefore limiting conditions for producing emulsions yielding suitabledeveloped images cannot be given. It .has, ho'wever, been found during the course of experiments that emulsions in accordance with the present invention containing silver chloride in the form of very fine grains give particularly good results, since this on development certain well-known developers give what are known as warm-toned images, that is, images-which are of a redor yellowish-red colour. I

, On the other hand, it has been found that i other development emulsions containing substances for modifying the quality of the blackness of the image during development are not suitable, as the added substance appears to interfere with the toning properties of the toning ingredients when these are added to the emulsion in accordance with the present invention.

A preferred process for the manufacture of a self-toning development emulsion according to the present invention comprises forming an emulsion consisting essentially of silver chloride and gelatine by precipitating the silver chloride ingan emulsionaccording to the invention:

A solution comprising gelatine, water, citric :acidand silver nitrate was made up at 110 F.

and to this was added a quantity of a solution of manganese chloridemore than sufiicient to precipitate all the silver in the form ofsilver chloride. The quantities were as follows:

Gelatine 24 gms.

Water -l 200 cc. 2 N citric acid- 5 cc. 2 N silvernitrate 10.0 cc. 2%N"manganese chloride 11.0 cc.

Emulsification was effected inthe usual wayand the emulsion shredded. The emulsion was then washed for one hour in 6 changes of water and melted out at 110 F.

A gold solution was made up by adding ammonium thiocyanate to sodium gold chloride in the presence of gum arabic, the following proportions being employed:

6% gum arabic solution 7.5 cos.

25% sodium gold chlorideiNaAuClrL- 0.75 ccs.

1.6% ammonium thiocyanate 7.5 ccs.

and this solution was then added to the above Washed emulsion, to which the following substances werealso added:

2 2: citric acid 5 cos. Gelatin 6- gms. Methylated spirit --20 7 cos. 5% chrome alum 2.5 ccs. 25% lead nitrate 2.0 ccs. 40% formalin Y 0.75 COS.

V The volume was, made up to 350 ccs. This formula gives a slow emulsion which may be increased in speed by the addition of suitable amounts of the agents normally used for increasing speed, c. g. thiosinamine or sensitizing dyes.

During the emulsification step described above silver chloride is precipitated from the solution of silver nitrate by the manganese chloride, and the soluble manganese nitrate formed is removed by the'washing which also removes any excess manganese chloride remaining. It will be noted that the emulsion is washed before the gold compound and other finals are added to it. It will .be appreciated that the substances added at the same time as the self-toning ingredients are those normally added to photographic emulsions to impart hardness to the gelatine and such desirable properties.

The emulsion is coated on paper in the usual manner.

toning ingredients a i Conveniently the following procedure is adopted in preparing the print. After an exposure to artificial light, comparable in duration to that given to ordinary gaslight papers, for example, for 4 or 5 seconds to a 100 watt /2watt type lamp at a distance of six inches with a normal negative, the paper is'passed' direct, i. e. without preliminary Washing, into a developer of the formula:-

Adurol 1. 25 gms. Sodium sulphite (crystals) 5 gms. Sodium carbonate (crystals) 10 gms. Potassium bromide 0.5 gms.

Water 550 During development a reddish image is produced. Thereafter the print is immersed in an acid stop bath (e. g. a one per cent solution of hydrochloric acid) for one minute, then washed for two minutes,and finally transferred to the fixing bath in which toning takes place. This bath may conveniently comprise a 30% solution of sodium thiosulphate to which may, if desired, be added a small proportion of ammonium thiocyanate. Immersion in the toning and fixing bath is continued until the desired shade of colour has been reached, and the print is then withdrawn and washed thoroughly before drying. The actual COS.

tone obtained depends upon the duration of ly warmertones can be obtained by using a weaker fixing bath of approximately 20% strength. The actual tone may be modifiedby the addition of more or less thiocyanate to the fixing bath.

Still colder tones may be obtained if desired by treating the print after removal from the developing bath and before fixing,.in a solution of common salt with or without potash alum until the colour has reached the desired tone, the print then being removed and fixed in thiosulphatein the ordinary way, or alternatively common salt may be added 'to the fixing bath.

If in the manufacture of the emulsion according to the formula given herein, the manganese chloride is replaced by sodium, ammonium, lithium or strontium chloride, an emulsion of substantially the same properties will be obtained. Where sodium, ammonium and lithium chlorides, or chlorides of other'metals which do not produce a scum of insoluble carbonate in the developer, are employed, the complete process may be carried out with some measure of success even if the emulsion is not washed before the addition of the gold and other finals, and there is no preliminary washing of the print before development. However, although the toning process is not prevented by the presence of the nitrates of sodium, ammonium and lithium or the like, improved results are obtainable when these are removed.

Variation in the tone and in the rate of toning may be obtained by varying the amount and/or composition of the toning agents added to the emulsion. r

I claim: a l. A self-toning photographic development emulsion comprising mainly silver chloride but gredient and a gold salt and a lead salt as self- 2. A self-toning photographic development emulsion comprising mainly silver chloride but no soluble silver salt as the light sensitive ingredient and a gold salt, a lead salt and a thiocyanate as self-toning ingredients.

3. A process for the production of self-toning photographic development emulsion comprising forming an emulsion containing essentially gelatine and silver chloride by precipitating the silver chloride from a soluble silver salt by means of a soluble chloride and then washing from the emulsion the non-silver salt formed by the reaction together with any excess soluble silver salts and soluble chloride, and then adding a solution containing gold salt and a lead salt as self-toning ingredients.

4. The process of claim 3 wherein a thiocyanate is also added as one of the selt-toning ingredients.

5. A process for the production of a self-toning photographic development emulsion comprising forming an emulsion containing essentially gelatine and silver chloride by precipitating the silver chloride in situ, washing from the emulsion any soluble salts, and adding to the emulsion as self-toning ingredients a gold solution made up by adding ammonium thiocyanate and a lead salt to gold chloride in the presence of gum arabic.

6. A method of producing a toned image which consists in exposing to light a paper bearing a self-toning photographic development emulsion comprising mainly silver chloride but no soluble silver salt as the light sensitive ingredient and a gold salt and a lead salt as self-toning ingredients, developing the exposed paper in a development solution to produce a reddish image and finally toning and fixing the image by immersing the print in a solution of sodium thiosulphate.

'7. The method of claim 6 wherein an adui'ol development solution is employed.

8. The method of claim 6 wherein a hydroquinone development solution is employed.

WILLIAM AMBLER BERRY. 

